RAID-Related Terms

SCSI-2

The second standard, and the most common today. You can mixSCSI-1 and -2 devices on one SCSI-2 bus because it's backward-compatible toSCSI-1. SCSI-2 offers much higher burst and sustained transfer rates (althoughthe standard is only 5MBps), with a clock speed of 20MHz.

Fast SCSI-2

Runs at 10MBps.

Wide SCSI-2

Runs at 10MBps but extends the data path to 16 or 32bits.

Fast and Wide SCSI-2

Runs at 20MBps over a 16-bit data path.

SCSI-3

Also known as Ultra SCSI (or Fast 20). It is fullybackward-compatible to SCSI-2 and uses 4-bit (deep) addressing. This newstandard extends performance to 40MBps.

Fast SCSI-3

Runs at 20MBps; cable length limits are the same asSCSI-2, unless you have differential wiring.

Wide SCSI-3

Runs at 40MBps. SCSI-3 is by nature "fast";doublewide uses 32 bits instead of 16.

SCSI-4

Also known as Ultra 2. It is a 64-bit standard designed for64-bit PCI and runs at 80MBps with a clock speed of 40MHz.

Deep SCSI

Uses 4 bits instead of 3 to identify devices on the bus,allowing for up to 15 total devices on a channel.

Single-ended wiring

Cable wiring scheme that is more prone to noisebecause all signal lines use a common ground. It has a 6-meter cablelength limit.

Differential wiring

Wiring scheme that uses signal/ground wire pairs,which reduces noise and allows for up to 25-meter cables. The twoversions of differential are low-voltage (LVDS) and high-voltage (HVDS). The oneyou choose depends on the cable length you want, data speeds, and other factors­HVDSis for SCSI-4. You cannot mix single-ended and differential devices on the samebus.